Morning
To clarify the options between the pumps the only real factor is output, in real terms that means required pressure and flow.
There is not really an option as such and they do not overlap, your requirements will decide which you need.
If you are planning up to 380-400bhp NA (not likely) or up to 350bhp SC, depending upon pressure, then the new unit covers all you need with all the advantages of a brand new unit, latest turbine design pump, VERY efficient using the same power as OE with a much higher output, very quick canister refill times of around 4-5 seconds even when delivering fuel at max power, quiet, full E85 compatibility including a new heavy duty E85 connector. (the OE Delphi units, along with several hundred other Delphi lines were made obsolete due to the overheating of the terminal block which has melted through the top to expose the fuel, these have all been replaced with a new design but not the Lotus unit which was special order.
We can also fit a wide body pump into this unit that takes you up to 380bhp at 60psi (3 bar rail + 1 bar boost)
If you need more fuel than above then the OE units can be converted to order and fitted with a suitable pump for your current and any future requirements.
An important part of the conversion is to change the connector block (as well as all the seals) to to the same design as the new pumps, this ensures E85 compatibility and future proofs the units.
The pumps themselves are also turbine and are selected upon requirement, once this is known the eductor jet is also resized and balanced to give the lowest refill times without effecting the back pressure of the return system. They are quiet, reliable and give a faster canister recharge that OE.
We are currently working on a dual channel pulse modulation controller that will allow the fitting of a higher output pump for all conversions which is controlled by an Ecliptech Shift-P2+ progressive display to control maximum output and also switch the pump to a lower output when below a certain RPM. This would cut fuel heating to an absolute minimum but allow complete flexibility over future requirements up to 800bhp+
Left hand cornering
A plague on most of the high output VX and Elises, it's caused by the tank design which in car orientation terms is wide (bad) not very high (bad) very short (good). On top of this the pump is positioned at the extreme left hand side but is not trapped, at 1G lateral the fuel will go to one end with the surface at 45 degrees, (imagine you hold the tank at 45 degrees and picture where the fuel would be) not hard to see that even with a lot of fuel in the tank you can still leave the pump unit out of the fuel which is where the canister comes in.
Part of the pump units design is to act as a reservoir for when fuel is not available, all well and good but the size of the canister is limited to what is commercially available, not for Lotus to order a custom fuel pump assembly and to be fair at normal powers 160bhp or so when designed it's not a problem as there is still enough fuel for 20-25 seconds at full power, enough for almost any long left or combination left hander.
The problem comes when you increase the fuel requirement as this will reduce the power on time, in the case of SC cars which have a higher BSFC and powers up to 400+ you can see how the available fuel could be down to a few seconds at maximum power. It's unlikely of course you would be at full power all the time but regardless you will always have less time than with a low output engine.
The best we can do in terms of pump units is to ensure the canister is always kept as full as possible and to make the canister as large as possible but still fit the OE tank.
Both units are way better than OE for refill times and the new units are also much taller, these go a long way to reducing fuel starvation to a limited number of corners/track the most notable is Zandvoort with it's left, then continuous left all the way up the hill. At +/- 300bhp without a trapped tank you simply will not have enough fuel in reserve without a quick right/left jiggle up the hill to charge the canister.
Walbro Conversions
Very good in there day but now not so ideal, we stopped using Walbro years ago as they are of an intermeshing gear type which is inefficient due to the high friction rates and noisy, even the new VHP Walbro is turbine though not suitable for the VX unless you are making 1000bhp! what we try to point out is that it isn't just a case of swapping the pump, a lot of other conversion work needs to be done if you are going to get the advantages and reliability mentioned above.
At the moment we re-convert about 4-5 units a year back from self converted Walbro units which suffer anything from burst rubber tubing, bleed back which means you have to prime the pump a few times, poor recharge as the eductor is no longer matched to the pumps output, and the noise which is a combination of a noisy pump and the eductor jet hitting the pump carcass. In almost all cases the wiring harness has not been completely replaced with suitable cable not to mention the continued use of a obsolete connector which is now taking even more power +5A or so.
Considering the nause of removing the tank/pump and the potential problems of a poor conversion/install it's probably not the best item on the car to save £99 on.
